1. Field of the Invention
The present invention relates in general to the field of electronics, and more specifically to a method and system for reducing standby power in an electronic power control system.
2. Description of the Related Art
Power control systems often utilize a switching power converter to convert alternating current (AC) voltages to direct current (DC) voltages or DC-to-DC. Switching power converters provide power factor corrected and regulated output voltages to many devices that utilize a regulated output voltage. Exemplary devices that utilize a regulated output voltage include lamps, such as light emitting diode and gas discharge type lamps, cellular telephones, computing devices, personal digital assistants, and power supplies.
Generally, a controller controls the conversion of power by a switching power converter. The controllers have an active mode to actively control the switching power converter when the switching power converter is providing power to a load. To save energy, some controllers also have a standby mode. During standby mode, the controller enters a low power consumption state because low power demands by a load connected to the switching power converter do not require the controller to control the switching power converter.
FIG. 1 depicts an electronic power control system 100 that includes a controller 102 that controls the operation of, and, thus, the delivery of power by switching power converter 104 to load 132. Voltage source 106 supplies an alternating current (AC) input voltage VIN to a full bridge diode rectifier 108. The voltage source 106 is, for example, a public utility, and the AC voltage VIN is, for example, a 60 Hz/110 V line voltage in the United States of America or a 50 Hz/220 V line voltage in Europe. The full bridge rectifier 108 supplies a rectified AC voltage VX to the switching power converter 104. Capacitor 110 filters high frequency components from rectified voltage VX.
To control the operation of switching power converter 104, controller 102 generates a control signal CS0 to control conductivity of field effect transistor (FET) switch 124. The control signal CS0 is a pulse width modulated signal. Control signal CS0 waveform 126 represents an exemplary control signal CS0. Each pulse of control signal CS0 turns switch 124 ON (i.e. conducts), and the inductor current iL energizes inductor 128. Diode 127 prevents current flow from link capacitor 130 into switch 124. When the pulse ends, the inductor 128 reverses voltage polarity (commonly referred to as “flyback”) and the inductor current iL charges link capacitor 130 through diode 127. The switching power converter 104 is a boost-type converter because the link voltage VLINK is greater than the rectified input voltage VX. Controller 102 operates the switching power converter 104 to maintain an approximately constant link voltage VLINK for load 132 and provide power factor correction. Load 132 can be any type of load that utilizes the link voltage, such as lamps, such as light emitting diode and gas discharge type lamps, cellular telephones, computing devices, personal digital assistants, and power supplies.
To control operation of switching power converter 104, controller 102 monitors a sense signal VX_SENSE, which represents the rectified voltage VX, and monitors a sense signal VLINK_SENSE, which represents the link voltage VLINK. Resistors 112 and 114 provide a voltage divider between the reference voltage VREF and the input voltage VX at node 116. VX_SENSE is the voltage across resistor 114, and, thus, represents the rectified voltage VX. Resistors 118 and 120 provide a voltage divider between the reference voltage VREF and the link voltage at node 122. VLINK_SENSE is the voltage across resistor 120, and, thus, represents the link voltage VLINK. Controller 102 uses the sense signals VX_SENSE and VLINK_SENSE to generate the control signal CS0 using well-known control circuitry.
When switching power converter 104 no longer needs switch 124 to conduct to supply the power requirements of load 132, the controller 102 enters standby mode. Thus, in standby mode, controller 102 does not generate control signal CS0 and thereby minimizes power usage. However, in standby mode, controller 102 still requires power to continually monitor the sense signals VX_SENSE and VLINK_SENSE in order to ascertain the state of the switching power converter 104. By monitoring the state of switching power converter 104, the controller 102 can determine when to exit standby mode and resume generating controls signal CS0. Thus, sense currents iVX_SENSE and iLINK_SENSE continue to flow during standby mode, which results in additional energy usage by electronic power control system 100 during standby mode. Controller 102 resumes in the active mode when power requirements of the load 132 indicate a need to resume operation of switching power converter 104.